1. Field of the Invention
The invention relates to a lens barrel, and more particularly to a lens barrel that solves flash issue and that does not need vent holes.
2. Description of the Related Art
A lens barrel of a conventional lens module has flashes on a parting line after injection molding. When the lens barrel is bolted with a holder, the flashes on an external thread of the lens barrel rub against an internal thread of the holder to thereby result in powder pollution, which is called a flash issue.
Referring to FIG. 1 and FIG. 2, a thread structure 1 (disclosed in U.S. Pat. No. 7,565,078 B2) is proposed to diminish powder pollution caused by the flash issue. Each circle of the thread structure 1 has a normal thread 101, and a partial withdraw thread 102 that is located along a longitudinal parting line 103.
When the thread structure 1 is assembled with an internal thread 301 of a holder 3, flashes at the parting line 103 do not rub against the internal thread 301, so that the powder pollution does not occur. However, a difference between the edge of the normal thread 101 and that of the partial withdraw thread 102 is greater than 0.03 mm in a radial direction, and thus forms a clearance surface 104 between an outer edge of the normal thread 101 and the partial withdraw thread 102, resulting in accumulation of powders on the clearance surface 104. That is, powders produced due to rubbing between the normal thread 101 and the internal thread 301 easily accumulate on the clearance surfaces 104, and fall off during repeated threading assembly and disassembly in rework processes which may result in pollution of an imaging sensor, such as a surface powder pollution issue of a complementary metal-oxide-semiconductor (CMOS) imaging sensor.
Moreover, formation of the clearance surface 104 between the normal thread 101 and the partial withdraw thread 102 can lead to the situation that the demand of torque in an assembling process is non-continuous torque.
As shown in FIG. 2, when an assembly, which is composed of the holder 3 and a camera lens 6 that includes a lens barrel 2 and a plurality of lenses 5, is installed on a plate 4 having an imaging sensor 401 thereon, the holder 3 is typically fixed on the plate 4 by applying a glue therebetween and then subsequently baking the glue. The holder 3 needs several vent holes 302 to discharge the hot air generated in the baking process. Thereafter, the vent holes 302 are sealed by filling with glue. FIG. 2 shows a condition before filling glue into the vent holes 302. During the glue applying and baking process, powders may fall into the vent holes 302 to result in surface powder pollution on the imaging sensor 401. Moreover, control of glue quantity is difficult. If the filled glue is insufficient, electro-magnetic interference to the imaging sensor 401 and electrostatic discharge issue may occur. If the filled glue is too much, it may overflow.